Research on infertility: definition makes a difference. The Cancer and Steroid Hormone Study Group

Although different definitions of infertility are used, research findings based on various definitions have not been systematically compared. To contrast the impact of five definitions of infertility on research findings, the authors analyzed data from the control group (randomly selected US women aged 20-54 years) of the Cancer and Steroid Hormone Study (1980-1983). For all definitions, an absence of recognized conception was the outcome of interest. Specifically, the authors examined the effect of various definitions of infertility on demographic characteristics of women classified as infertile, prevalence of a history of infertility, age at infertility classification, and cumulative incidence of conception after infertility classification. Results indicated that women classified as infertile by definitions based on unprotected intercourse for 12 months and unprotected intercourse for 24 months were more likely to be black, less educated, and classified as infertile at younger or older ages that women classified by alternative definitions. The prevalence of a history of infertility ranged from 6.1% (physician diagnosis) to 32.6% (unprotected intercourse for 12 months). For the definitions based on unprotected intercourse for 12/24 months and for physician diagnosis, the cumulative incidence of conception by greater than 120 months after infertility classification was 86.3%, 76.7%, and 75.4%, respectively. The authors conclude that the definition of infertility has an impact on research findings related to which and how many women are classified as infertile, the age at infertility classification, and the probability of future conception.